The present invention generally relates to a binary image signal processing apparatus. More specifically, the present invention is directed to an apparatus capable of detecting coordinates of changing points in input binary image signals at high speeds, required when the binary image signals such as facsimile signals are data-compressed.
In general, to shorten data transfer time periods and also to reduce storage capacities of binary image data, various binary image data compressing systems have been widely utilized. The modified Huffman coding system and the modified READ system are known as the typical image data compressing system. In any of these data compressing systems, coordinates of changing points contained in binary image signals must be detected. That is, detections should be made of coordinates of pixels of binary images, which are transferred from white to black, or from black to white. Conventionally, the detection of this changing point is carried out by comparing the present pixel value with the preceding pixel value, as described in U.S. Pat. No. 4,245,257.
The above-described conventional changing point detecting system has a problem in that since the changing point detecting process is performed on a bit by bit basis, lengthy detecting time is necessarily required. As a consequence, this changing point detecting system causes the binary image signal coding speeds to be lowered.